Copper-base alloy for high precision resistors

ABSTRACT

An alloy especially useful for high precision resistor material consists essentially of about 8 to about 14% (by weight) of manganese, about 6 to about 10% (by weight) of gallium, and the balance being copper. Small amounts of germanium, indium, nickel and/or aluminum may be present. The alloy is characterized by having in combination extremely low first and second temperature coefficients of resistivity, extremely low thermal EMF vs. copper, extremely high time stability of all properties, excellent workability and high corrosion resistance.

United States Patent [1 1 Blinov et al.

[ COPPER-BASE ALLOY FOR HIGH PRECISION RESISTORS [22] Filed: Sept. 20, 1973 [21] Appl. No.: 399,119

Related US. Application Data [63] Continuation-impart of Ser. No. 77,014. Sept. 30,

I970, abandoned.

[52] US. Cl. 75/161, 338/334 [51] Int. Cl C22c 9/00, C220 9/06, HOlc 13/00 [58] Field of Search 75/153, 161; 338/334 [56] References Cited UNITED STATES PATENTS 4/1949 Brenner 75/161 X 6/1969 Thielmann 75/153 X 1 Nov. 12, 1974 OTHER PUBLICATIONS Primary Examiner-C. Lovell Attorney, Agent, or Firm-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT An alloy especially useful for high precision resistor material consists essentially of about 8 to about 14% (by weight) of manganese, about 6 to about 10% (by weight) of gallium, and the balance being copper. Small amounts of germanium, indium, nickel and/or aluminum may be present. The alloy is characterized by having in combination extremely low first and second temperature coefficients of resistivity, extremely low thermal EMF vs. copper, extremely high time stability of all properties, excellent workability and high corrosion resistance.

8 Claims, N0 Drawings RESISTORS CROSS-RELATED APPLICATION This application is a continuation-in-part of our earlier application, Ser. No. 77,014 filed Sept. 30, 1970 now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to copper-base alloys and more particularly to alloys which are especially useful as high precision resistor material.

Such an alloy shall meet the following requirements:

1. Its resistivity shall be sufficiently high (not substantially lower than 30-35 11. Ohm-cm); .2. Its first and second temperature coefficients of resistivity (i.e. first and second derivatives of resistivity with respect to temperature) shall be as low as possible;

3. its resistivity shall remain constant over a prolonged period of time;

4. Its thermal electromotive force (EMF) versus copper shall be as low as possible;

5. It shall possess a high degree of corrosion resistance in the operating temperature range;

6. Its workability shall be good enough to produce readily sufficiently fine wires, strips, ribbons etc.

Among the copper-base alloys known in the art the most suitable for use as a high precision resistor material are the following alloys:

(the symbol below and throughout the specification and the claims means weight unless otherwise specified) a. Alloys known under the trademark Manganin. Such alloys contain 2 to 4 percent nickel and 10 to 13 percent manganese, the remainder being copper. Manganin type alloys are disclosed e.g. in the Alloy Digest, Filing Code Cu-l26 and in US. Pat. No. 3,451,808 to Thielmann, lines 26 to 53 in the col. 1 and No. 1 ,alloy in'the table on col. 3-4;

b. Therlo alloy comprising 5.5% aluminum, 9.5%

manganese, the remainder being copper. This alloy is disclosed eg in NBS Circular 470, p. 4 (reprinted in vol. 3 of NBS Special publication300, see p. 155), see also the above-mentioned U.S. Pat. to Thielmann, lines 54-63 in the col. 1; 1 c. Copper-manganese-germanium alloys comprising 6 to 22% manganese and 0.1 to 8% germanium optionally also small amounts of some other metals (tin to 3%, antimony to 1%, arsenic to 0.5%, gallium to indium to 1%, aluminum to 5%, zinc to 5%, nickel to 5%, all these metals together should not exceed about 10%), the remainder being copper. Such alloys are disclosed by Thielmann (U.S. Pat. No. 3,451,808, British patent specification No. 1,155,051 etc.) and by I-Iirayama (Japanese patent specifications No. 34-2407 and No. 37-11404 as well as his monograph published as No. 618 of the Researches of the Electrotechnical laboratory series, Tokyo, Oct. 1961, see especially p. 5 of the English Synopsis attached to this monograph).

However, none of the alloys known in the art do fully meet the above cited requirements.

The disadvantages of the previously known Manganin and Therlo alloys are described e.g. in the above-mentioned US. patent to Thielmann.

Copper-manganese-germanium alloys disclosed by Thielmannand by I-Iirayama also have appreciable disadvantages.

Such alloys with high germanium content (over 3 percent) while having good values of temperature stability of resistance, do not possess sufficient stability of electrical properties in time. Their thermal EMF vs. copper is relatively high. And last but not least such alloys cannot be readily worked, they are fragile, and forging of ingots to make rods etc. is inherently tied with considerable amount of waste. Nos. 3 and 4 alloys of the Thielmann patent, containing 6 and 8% of germanium respectively, are exemplary for such alloys. As maybe seen from the table on col. 3-4 of the Thielmann patent, thermal EMF vs. copper is for each of these alloys about 2.5 times as high as that for Manganin. Such relatively high values of thermal EMF vs. copper preclude the possibility of performing highest precision measurements with employment of resistors made from these alloys. It is worth noting also that if copper-base alloys have high thermal EMF vs. copper (as is the case for the alloys Nos. 3 and 4 of Thielmann patent) this indicates the appreciable discrepancy of Fermi levels (chemical potentials) for the alloy and for copper which in turn causes the instability of the alloycopper system (e.g., instability of resistance of the whole resistor leads terminals system). A high germanium content in a copper-base alloy necessarily implies a relatively high thermal EMF of such alloy vs. copper (as is stated e.g. by Thielmann in the abovementioned British patent specification No. 1,155,051, page 2, lines 5 to 9). 1n the above-mentioned Japanese patent specification No. 34-2407 it is explained (see page 2, left column, lines 1 to 3 and also page 2, right column, lines 7 to 13) that copper-manganese alloys with a germanium content higher than 3 percent show decomposition of solid solution, and, as a corollary, time instability and insufficient ductility. Therefore, the alloys with high germanium content, despite good temperature stability of their resistance, are apparently not very useful for making resistors of highest precision.

On the other hand, the resistivity of the copper-manganese-germanium alloys with low (under 3 percent) germanium content (eg of alloys Nos. 5 to 14 of the Thielmann patent and of the alloys disclosed in the above-mentioned Hirayama publications) is dependent in a much higher degree on the temperature. As may be seen from the drawing in the Thielmann patent, the resistivity variations in the temperature range 20 to 50C are for alloys Nos. 5-14 within the limits 0.0025 to 0.008 percent. These limits are nearly 10 times worse than those for Thielmann alloys Nos. 3 and 4, while nearly 4 to 1.5 times better than those for Manganin. The first temperature coefficient of resistivity a, for the alloys disclosed in the above-mentioned Japanese patent specification No. 34-2407 and in the Hirayama monograph is practically equal to zero, but

the second temperature coefficient of resistivity B isv not sufficiently low. a, and [3 are coefficients in the equation:

t o( 01 o) +8 0)) where t is a standard or reference temperature (usually 2,,

= 20C or z 25C) R, is resistivity at temperature t and R, is resistivity at temperature 2.

As stated by Hirayama, the [3 values for his alloys vary from 0.35'l0 C to 0.6-l' C It is highly desirable to reduce the ,8 values even more. The lower the [3 value, the lessthe variation of resistivity in the same temperature range. Moreover, increasing the [3 values hardensthe requirements for thermal treatment of alloy because variations in the thermal treatment result in shifting of the position of the upper point of the R-t curve, and the more flattened the curve, the less the effect of 'this'shifting on the resistivity of the alloy at standard temperature t,,.

The resistance to corrosion and time stability for all the mentioned copper-manganese-germanium alloys are not fully satisfactory.

SUMMARY OF THE INVENTION The present invention aims to avoid the above listed disadvantages of thealloys known in the art and to provide an alloy for highest precision resistors which will more fully meet the requirements for alloys of such a a kind.

x 0 or very close to 0 for alloys having a manganese content of about 6 percent, the gallium content being equal to about 3 to 5 percent. If the gallium content is increased to exceed 5 m6 percent, the amount of manganese required to obtain [3 0 is gradually increased, and thus approaches the amount of manganese required to obtain a 0.'This may be explained by the fact that exactly when the gallium content exceeds 5 to 6 percent in the alloy, a ternary intermetallic compound of copper, manganese, and gallium begins to be formed.

Small amounts of germanium, indium, nickel and/or aluminum (which will be referred to hereafter as secondary alloying metals) may be added. Most of the preferred embodiments of the proposed alloy may be described as an alloy substantially conforming to the stoichiometric formula Cu Mn with part of the manganese atoms (preferably not less than one third and not more than'one half of the manganese atoms) substituted by gallium atoms or by gallium atoms and atoms of the mentioned secondary alloying metals (the amount of gallium atoms shall be not lower than the amount of atoms of the secondary alloying metals). In other words, the copper content shall be about 83.3 atomic percent, manganese content 8.3 to 11.1 atomic percent, gallium content 2.8 to 8.4 atomic percent, and the content of secondary alloying metals up to 4.2

atomic percent. As we have found the copper content The secondary alloying metals do not substantially affect the properties of the alloy. Germanium in an amount not exceeding 0.5'percent (by weight) serves as a deoxidizing agent and facilitates producing of sound castings and obtaining of desired component proportions. An addition of indium (not more than 1.5 percent) accelerates the process of alloy stabilization and enhances its corrosion resistance. Substituting a portion of gallium by aluminum reduces the cost of the alloy and increases its ultimatetensile strength. The addition of nickel further improves the corrosion resistance and also raises the tensile strength of the alloy, adding of aluminum and/or nickel do not cause appreciable worsening of the electrical properties of the alloy providing that the total amount of secondary alloying metals is not in excess of 5 percent.

It is therefore one object of the present inventionto I provide an improved alloy which is especially useful for highest precision resistors and possesses in coinbina-' DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Other objects of the present invention anda'dvantageous features thereof will become apparent from the description. I g Y The proposed alloy may preferably be produced by fusing the initial constituents in a crucible placed in a 1 high frequency electric furnace under a protective layer of borax or in vacuum, or else, in an inert gas atmo'sphere, said-crucible being made of alumina, with the subsequent casting of the product into copper molds. Wire and strip are produced from this alloy by plastic deformation. The alloy constituents preferably may be so selected as to correspond to stoichiometric formula of Kurnakov compound Cu Mn, wherein part of manganese is substituted by gallium or by gallium I and at least one of the following secondary alloyingv metals: germanium (till 0.5% by weight), indium (till 1.5%), aluminum (till 5%) and nickel (till 5%). The

total amount of the secondary alloying metals should not be in excess of 5 percent.

To make the present invention more'fully apparent four alloy compositions are described below which are exemplary for our alloys.

The chemical composition of the alloys in Examples 1-3 is presented following the chemical analysis of the melt or a fresh cast ingot. The chemical composition of the alloy of Example 4 is presented following the chemical analysis of a wire made of the alloy. The chemical composition of the wire may slightly differ from that of the ingot it is made of, namely: the proportion of manganese in the wire may be by 0.2 to 0.5 percent lower f than in the ingot, the content of the other elements being accordingly higher.

EXAMPLE 1 An alloy containing 12% manganese, 6% gallium, 1% indium, 0.5% germanium, 80.5% copper (or, in atomic l3.95.50.5-0.479.7% respectively). The resistivity of this alloy is p 50 1. Ohm 'cm, first and second temperature coefficients of resistivity are:

01,, 6.10- "C p -0.04-- cthermal EMF vs. copper (in the 40C temperature range) AE/Az -0.23 p v/c EXAMPLE 2 An alloy containing 9% manganese, 6.6% gallium, 84.4% copper (or, in atomic l0.3-6.0-83.7% respectively) has the following electrical properties:

EXAMPLE 3 An alloy containing 9.2% manganese, 6.6% gallium, 0.2% germanium, 84% copper (or, in atomic 10.5 6.0 0.2 83.3% respectively). Electrical properties of this alloy are as follows: p 37 Ohm-cm, 0: 0.2'l0 "C", B=0.27'l0' C, AE/At=0.3 p. V/C.

EXAMPLE 4 An alloy containing 8.4% manganese, 9.8% gallium, 81.8% copper (in atomic 9.7 8.9 81.4% respectively). This alloy has the following properties:

p 40 [L Ohm-cm, 01 0.210 C, [3 00910 T, AE/At -0.3 p. V/C.

Thus the resistivity of our alloys is substantially the same as that of the known alloys. Temperature stability of resistance is as good as that for alloys with high germanium content (Nos. 3 and 4 alloys of Thielmann patent; the disadvantages of these alloys are discussed above). The value of thermal EMF vs. copper is for our alloys considerably lower than that for these alloys and even than for all known in the art precision resistor alloys except Therlo.

The resistivity of our alloys does not vary more than by 1 10' per year (by 1'10 percent) providing proper thermal treatment and artificial aging are carried out as is well known in the art.

Our alloys have good mechanical and technological properties and excellent workability. They may be readily forged without significant amount of waste. From these alloys may be readily produced the finest wires, ribbons, strips etc. Ultimate tensile strength is 440-460 N/ mm Elongation of wire made from our alloys equals for 0.5 mm diameter wire 34 to 45%, for

microns diameter 23-28 percent (for Manganin 30 and 15 percent respectively, for alloys with high germanium content not more than 10 percent for 25 microns diameter wire).

Corrosion resistance of our alloys is not lower than that of Therlo" and considerably higher than corrosion resistance of Manganin and copper-manganesegermanium alloys.

We claim:

1. An alloy especially useful as material for precision resistors, said alloy consisting essentially of between about 8% and about 14% of manganese, between about 6% and about 10% of gallium, and the remainder being copper.

2. An alloy according to claim 1 wherein the copper content is about 84.4%, themanganese content about 9% and the gallium content about 6.6%.

tional secondary alloying metals in the amounts as given:

up to about (percent) Germanium 0.5 Indium l.5 Aluminum 5 Nickel S the total amounts of said secondary alloying metals not substantially exceeding 5 percent, and the remainder being copper.

5. An alloy according to claim 4, wherein the copper content is about 80.5%, the manganese content about 12%, the gallium content about 6%, the indium content about 1%, and the germanium content about 0.5%.

6. An alloy according to claim 4, wherein the copper content is about 84%, the manganese content about 9.2%, the gallium content about 6.6%, and the germanium content about 0.2%.

7. An alloy especially useful as material for precision resistors, said alloy conforming to the stoichiometric formula Cu Mn with not less than one third and not nium, indium, aluminum and nickel.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,847,602 DATED November 12, 1974 "KINVENTOR(S) I Boris Vladimirovich Blinov et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cover page, in amend "proezd" to read:

the heading,

inventors: prospekt (line 3) Column 2, line 2 amend "Thielmannand" to read:

Thielmann and Column 5, line 10 amenofi to read:

-- AfE/At -0.o23 u v/c Signed and Scaled this A ttest:

RUTH C MASON DONALD W. BANNER Altesting Officer Commissioner of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,847,602 DAT'ED November 12, 1974 ---INV ENTOR(S) 2 Boris Vladimirovich Blinov et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent. are hereby corrected as shown below:

Cover page, in amend "proezd" to read:

the heading,

inventors: prospekt (line 3) Column 2, line 2 amend "Thielmannand" to read:

- Thielmann and Column 5, line 10 amend to read:

AE/At 0.023 Ll V/C Signed and Scaled this Fifth D3) of September I978 [SEAL] A IteSt:

R MASON DONALD W. BANNER Attesting Oflicer Commissioner of Patents and Trademarks 

1. AN ALLOY ESPECIALLY USEFUL AS MATERIAL FOR PRECISION RESISTORS, SAID ALLOY CONSISTING ESSENTIALLY OF BETWEEN ABOUT 8% AND ABOUT 14% OF MANGANESE, BETWEEN ABOUT 6% AND ABOUT 10% OF GALLIUM, AND THE REMAINDER BEING COPPER.
 2. An alloy according to claim 1 wherein the copper content is about 84.4%, the manganese content about 9% and the gallium content about 6.6%.
 3. An alloy according to claim 1 wherein the copper content is about 81.8%, the manganese content about 8.4% and the gallium content about 9.8%.
 4. An alloy especially useful as material for precision resistors, said alloy containing between about 8% and about 14% manganese, between about 6% and about 10% gallium, and at least one of the following additional secondary alloying metals in the amounts as given:
 5. An alloy according to claim 4, wherein the copper conTent is about 80.5%, the manganese content about 12%, the gallium content about 6%, the indium content about 1%, and the germanium content about 0.5%.
 6. An alloy according to claim 4, wherein the copper content is about 84%, the manganese content about 9.2%, the gallium content about 6.6%, and the germanium content about 0.2%.
 7. An alloy especially useful as material for precision resistors, said alloy conforming to the stoichiometric formula Cu5Mn with not less than one third and not more than one half of the manganese atoms substituted by gallium atoms.
 8. An alloy according to claim 7, wherein not more than one half of the gallium atoms are substituted by atoms of at least one of the following metals: germanium, indium, aluminum and nickel. 